The present invention generally relates to methods and equipment suitable for use when assembling and disassembling turbomachines. More particularly, this invention relates to a method and system capable of installing and uninstalling inner turbine shells of a turbine engine.
In the hostile operating environments of gas turbine engines, the structural integrity of turbine rotor wheels, buckets, and other components within their turbine sections is of great importance in view of the high mechanical stresses that the components must be able to continuously withstand at high temperatures. For example, the regions of a turbine wheel forming slots into which the buckets are secured, typically in the form of what are known as dovetail slots, are known to eventually form cracks over time, necessitating monitoring of the wheel in these regions. The ability to detect and repair cracks is desirable in order to avoid catastrophic failure of a turbine wheel. While a turbine rotor can be completely disassembled to gain access to its individual components, inspection and maintenance techniques that can be performed with limited disassembly are preferred to minimize downtime, such as to fit within outage schedules of a land-based gas turbine engine employed in the power generating industry.
The construction of turbine sections that utilize multiple shells has become a common approach for facilitating the on-site maintenance of land-based gas turbine engines. A particular example is a dual shell design used for gas turbine engines manufactured by the General Electric Company, a notable example being the 9FB, 9H and 9FB.05 class gas turbines. As known in the art, turbines having this type of construction include casings, shells and frames that are split on the machine horizontal centerline, such that upper halves of the casings, shells and frames may be lifted individually for access to internal parts of the turbine. For example, by lifting the upper half of a turbine shell, the turbine rotor wheels, buckets and nozzle assemblies can be inspected and possibly repaired or replaced without necessitating removal of the entire turbine rotor. Prior to shell removal, proper machine centerline support using mechanical jacks is necessary to assure proper alignment of the rotor, obtain accurate half-shell clearances, etc.
With the use of a dual shell design as described above, the need to remove the turbine rotor from the inner turbine shell for the purpose of inspection and maintenance is often reduced or eliminated, with the result that downtime can be minimized by allowing the rotor and its components to be inspected and maintained at the same time that other internals of the rotor section are inspected and maintained. However, while the removal of the upper half of the turbine shell provides ready access to the exposed portions of the rotor wheels and buckets, access to those portions of the rotor wheels and buckets located in the lower half of the turbine shell is complicated by the presence of the lower half of the turbine shell. The location of the lower turbine shell and the precision of its installation in the turbine section present significant challenges to its removal and reinstallation for the purpose of conducting a complete inspection of the turbine section.
In view of the above, it would be desirable if a method existed that was capable of installing and uninstalling the lower inner turbine shell of a gas turbine engine.